Gas phase polymerization converts a gaseous monomer into granular solids. The gaseous monomer, and optional comonomer(s), are introduced under pressure into a reaction vessel, i.e. reactor, containing a catalyst and optional activator. Once polymerization begins, the monomer molecules diffuse to the growing polymer chains within the reactor. The resulting polymer can be obtained as a granular solid which can be fluidized within the reactor, along with the monomer and catalyst. Polymerization can include the use of induced condensing agents (“ICAs”) in order to increase the production rate of the polymer. However, the presence of ICAs in a polymerization reaction reduces the temperature at which the polymer begins to become “sticky.” Polymer stickiness causes polymer particles within a polymerization reactor to begin to stick together, which can lead to polymer buildup within the reactor, which in turn causes process upsets, e.g. reactor shutdown. The buildup of polymer is usually referred to as agglomeration, chunking, or sheeting of the polymer within the reactor.
Monitoring various reactor parameters can provide an indication or warning as to the potential for or the presence of polymer stickiness within the polymerization reactor. Typical methods or systems used for monitoring the degree of polymer stickiness include monitoring acoustic conditions with acoustic sensors and monitoring a stickiness control parameter of the polymer being produced within the reactor. Monitoring acoustic conditions requires producing a series of polymers under “dry” conditions, i.e. without ICAs, in order to generate calibration curves for the acoustic sensors, which is time consuming and must be repeated from time to time in order to check for acoustic sensor drift. Furthermore, acoustic condition sensors require frequent calibration in order to assure that accurate acoustic conditions are being acquired. Monitoring the stickiness control parameter is prone to inaccuracies as well, which are caused by one or more inaccurate measurements such as reactor temperature, reactor composition, and polymer properties, e.g. melt index and density.
There is a need, therefore, for improved systems and methods for monitoring a polymerization reaction to determine the degree of polymer stickiness.